1. Field of the Invention
This invention relates to thrust bearings, and in particular, to a non-tilting thrust bearing having a hydrostatic fluid film supporting the bearing pad away from its associated housing.
2. Description of the Prior Art
A thrust bearing is a device adapted to support a rotating shaft and to accommodate a load imposed thereon directed along the axis of the shaft. In general, the thrust bearing device comprises a housing completely surrounding the rotating shaft and supporting therewithin a bearing pad disposed in a bearing relationship with a thrust runner securely affixed to the shaft. A suitable lubricating fluid is provided and a hydrodynamic fluid film is generated between the bearing pad and the thrust runner when the shaft is rotating to provide a bearing surface on which the shaft may freely rotate and to support the shaft away from the bearing pad.
In the prior art, the bearing pad is physically affixed to the associated housing, most commonly by the provision of a pivoting contact about which the bearing pad tilts in order to facilitate generation of the hydrodynamic film. It has been found that the disposition of a high pressure layer of fluid film from the hydrodynamic layer exerts a force on the bearing pad which, when combined with the reactive force imposed upon the bearing from the pivotal contact, leads to a premature failure of the bearing pad.
The typical prior art bearing pads have been shown to deform due to the hydrodynamic oil film pressure acting on the upper surface of the pad between the pad and the thrust runner and also due to the thermal gradient which occurs across the pad thickness. The thermal gradient is produced by the heat generated within the hydrodynamic film which causes the upper surface of the pad to be exposed to a higher temperature than the temperature at the lower surface of the pad.
As a greater axial load is applied to the bearing pad, an increased deformation occurs necessitating an oil film pressure distribution exhibiting a sharp peak located at approximately the center of the pad. Such a pressure distribution increases the pressure force acting on the upper surface of the pad and also increases local heating at the pad center. The combination of the compressive stress due to the higher pressure force within the oil film and the high temperature at the pad surface ultimately causes plastic deformation of the bearing pad, with complete failure the most probable result.